Wireless networks and systems are becoming increasingly popular. But wireless communications are constrained due to a lack of available, interference free spectrum that may be used for reliable communications within a geographic area.
To enhance the availability and reliability of interference free spectrum, procedures that are governed by regulatory agencies (e.g., the Federal Communications Commission (FCC) in the United States) have been developed for allocating and using spectrum. In the U.S., for example, there are two general classes of spectrum, including licensed spectrum and unlicensed spectrum. With respect to the licensed spectrum, the FCC licenses spectrum in a primary spectrum market to Commission licensees. A secondary market exists for the Commission licensees to sublease spectrum for use by other parties. With some narrow exceptions (e.g., government priority rights), licensed spectrum is exclusively reserved for the corresponding Commission licensee and any subleasee(s).
Unlicensed spectrum may be used without a license and by virtually any party, but regulations on the spectrum may be imposed. Exemplary unlicensed spectrum includes industrial, scientific and medical (ISM) bands and information infrastructure (UNII) bands. These bands are open to all users provided the users comply with certain regulations. In the U.S., these regulations are known as FCC Part 15. Traditionally, these bands have been used for microwave ovens, cordless phones, low powered wireless remote controls, and similar devices. Recently, with the advent of IEEE 802.11 (commonly known as WiFi), these bands have become very popular for computer communications and mobile data communications activities, as well as for point-to-point and point-to-multipoint applications. As the number of installations and users of these applications has increased the unlicensed ISM and UNII spectrum bands have become very crowded.
Other unlicensed spectrum includes spectrum that has been freed by the conversion of analog television (TV) broadcasts to digital TV broadcasts. This conversion has freed spectrum channels for use by unlicensed radio systems to offer various services, such as mobile communications and Internet access. The available spectrum bands are commonly referred to as TV white spaces, which are made up of the guard bands and unused TV channels between channel 2 and channel 51 (corresponding to 54 MHz to 698 MHz).
To avoid interference with digital TV broadcasts and other incumbent systems, such as wireless microphone systems, radios that use the TV white spaces (referred to as TV white spaces devices or TVBDs) are required to register and receive a channel map of available channels that may be used for the communications activity of the radio system. Current regulations require these radio systems to register every twenty-four hours. Also, for mobile radios, if the radio moves into a new location, a new registration is required. Other regulations on the radios are present, such as transmitted power limits for different types of radios. Additional information regarding the regulation of TV white spaces may be found in FCC 08-260, Second Report and Order and Memorandum Opinion and Order, Adopted Nov. 4, 2008 and Released Nov. 14, 2008, the entirety of which is incorporated herein by reference. Similar proposals have been made in places other than the United States. For example, Ofcom in the United Kingdom has described access to certain spectrum by cognitive radios in “Digital Dividend: Cognitive—Access Consultation on License-Exempting Cognitive Devices Using Interleaved Spectrum,” published Feb. 16, 2009.
To efficiently use licensed spectrum, a network deployed by the licensee may make use of spectrum sharing techniques (also referred to as frequency sharing techniques). Most spectrum sharing techniques are embedded in the physical layer or the media access control (MAC) layer of a radio device's operating protocol. Exemplary types of spectrum sharing include frequency division duplex (FDD) and time division duplex (TDD). More specific exemplary standards for spectrum sharing include code division multiple access (CDMA) and orthogonal frequency division modulation (OFDM).
An example network that may use spectrum sharing is a network deployed by a mobile telephone service provider. Individual radios (e.g., mobile telephones and other supported client devices) in the network may “share” the spectrum by using different spectrum sharing “codes” that are assigned by network host devices. The codes govern when the radios may transmit and receive data and/or the frequency bands that are employed for wireless communications.